Diecast screwthreaded inserts and method of making them

ABSTRACT

A screwthreaded insert comprises a series of generally cylindrical body portions provided with inclined ribs or teeth, with the teeth of one portion extending in the opposite direction to those of the next adjacent portion, and the successive toothed portions being separated by grooves. The fastener is made by diecasting, and a pair of flats is formed on opposite sides of a diameter of the body.

This application is a continuation of application Ser. No. 011,390,filed 2/5/87, now abandoned, which itself is a continuation ofapplication Ser. No. 780,644, filed Sept. 26, 1985, now abandoned.

This invention relates to screw-threaded inserts intended forinstallation in bodies of thermoplastics material by any of varioustechniques.

BP No. 1279452A shows a fastener for ultrasonic installation, which isgenerally cylindrical having three portions of successively largerdiameter, with intervening plain grooves of a common smaller diameter.The second and third of the large diameter portions are provided withribs or teeth extending helically, and the two toothed or ribbedportions are of opposite hand. That is to say, viewed from one end ofthe fastener, one portion has the helices extending clockwise in travelalong the length of the fastener in one direction, whereas the otherportion has the helices extending anti-clockwise in travel along thefastener in the same direction. When the fastener is embedded in theplastics material, the surrounding material substantially fills thespaces between the teeth and also the grooves along the length of thebody. The material in the grooves provides resistance to pull-out but noresistance to turning, and the opposite hand of the two sets of teethprovide the resistance to turning. For example, if both sets were to bemade of the same hand, they would act like a screwthread and a turningload in the appropriate direction would tend to unscrew the insert fromthe plastics body.

Whilst the said BP No. 1279452-A describes the ultrasonic installation,using high frequency vibrations to cause the plastics to "flow", GBNo.2039660B describes a fastener having ribbed portions of opposite handat different axial locations, which is suitable for installation inappropriate materials by local heating to cause the plastics to flow.

FP No. 7918524 discloses a fastener for insertion into plastics materialprovided with a flat face formed on the periphery of the component, forexample by a cutting operation, so as to provide an extra resistanceagainst rotation.

These fasteners must be made on automatic lathes from bar stock at veryhigh speeds in order to be economically acceptable, but because of thenumber of separate operations, what is now seen to be high productioncost is inevitable, although in fact the cost has been accepted in thepast. But forming the flat to give the additional anti-rotational holdas in the mentioned French Patent cannot be done on the automatic latheand requires a separate operation which is even more expensive toproduce.

The object of the present invention is to provide an improved design offastener which is capable of production at only a fraction of theproduction cost.

In accordance with the invention a fastener is made by die-castingmaterial in liquid form to create a series of successive body portionsof different transverse widths of which at least one is provided withribs or teeth or and with a pair of generally diameterically relatedsubstantially planar surfaces extending generally along the length ofthe fastener, said fastener having a screw-threaded portion.

It is within the scope of the invention, at one extreme, to make afastener where all of the body portions are of circular cross-sectionapart from the flat surfaces: that is to say the toothed body or bodiesmay have a cross-sectional shape defined by two mouth-to-mouth arcs ofthe same radius on a single centre of curvature, ends of the arcs beingjoined by parallel secants of a circle.

The ribs may be helically extending, and two successive portions mayhave helices of opposite hand, but it is within the scope of theinvention to use axially extending ribs, circumferentially extendingribs, or e.g. knurled teeth arranged in any desired pattern.

At the other extreme, the bodies may be of triangular cross-section. Anyintermediate shape may be employed such as square, polygonal or a shapedefined by a series of curves of larger radius than half the maximumwidth.

These possibilities occur because the two constraints on design whichusually limit the fastener manufacture are removed: the fastener is notto be manufactured on a lathe, nor inserted by a rotary motion.

The die-casting is effected in die cavities which meet at a diametricplane of the fastener, and the flats are inter-sected by said plane.Preferably they are bi-sected.

Die-casting per se can provide far greater production rates, because iteliminates the steps necessary in machining bar, of producing thevarious different diameters from the bar and forming the teeth or ribs.The teeth or ribs and the different diameter portions are formed by thedimensions of the die cavity.

However, it has been found impossible to produce a fastener according toeither of said previous Patents as shown in the drawings of said Patentsby die-casting.

Fasteners of the kind in question are as mentioned provided with ascrewthreaded portion. This may be internally provided, so as to make aninsert nut, or externally provided so as to make an insert stud. It ispreferred to cut the screwthread in a subsequent operation. The flatsprovided by the invention provide a convenient gripping surface whilethe screw cutting is carried out.

Additionally, the fastener of the invention may optionally be providedwith a non-circular head further to facilitate gripping duringscrewthread forming.

Another surprising advantage of the present invention, over and abovethe increased production rates which are possible and greatly reducedcosts which then occur, is that it offers greater flexibility in designof the shape and position of the ribs and teeth as well as of the bodyshape as previously discussed. When those ribs or teeth are to beproduced by a knurling operation, a symmetrical rib which is moreovergenerally located at 45° to the axis of the fastener is most easilyproduced. Since the teeth of the die-cast fastener are only producedonce (on the original mould for example by a spark erosion operation)instead of on each fastener there is no limit in this direction. It istherefore possible and is preferred to provide an assymmetric tooth orrib of which the cross-section has a steeper flank, nearer to the planenormal to the axis of the fastener, towards the end of the fastenerwhich lies on the surface of the material when the fastener isinstalled, and a gently inclined flank, in other words one at arelatively great angle to the said plane directed towards the pilot endof the fastener which is first inserted into the material. By thesemeans, the fastener can provide a greatly improved pull-out load becausethe teeth can contribute much more to this as well as, and withoutdetracting from, the anti-rotational hold provided by the teeth.Insertion is also simplified by this. Hence, surprisingly, a technicallyimproved fastener can be produced more rapidly and at a fraction of theoriginal cost of the fastener shown in said prior Patents.

The foregoing discussion of asymmetry assumes that the fastener issingle-ended. It may then comprise two or more two ribbed portions ofsuccessively greater diameter towards the head end which is to lie onthe surface of the article in which the fastener is installed. Where thefastener is to be double-ended, so that it is immaterial which end isinserted and the fastener is symmetrical about a mid-point along itslength, the toothed or ribbed portion may be of uniform diameter andthen it is preferred to employ a symmetrical tooth/rib profile.

The invention is more particularly described with reference to theaccompanying drawing wherein:

FIG. 1 is a plan view of a fastener made according to the presentinvention;

FIG. 2 is an elevation of the same;

FIG. 3 is an elevation taken at right angles to the elevation of FIG. 2;

FIG. 4 is a cross-section taken on the line 4--4 on a greatly increasedscale;

FIG. 5 is a view similar to FIG. 2 of a modified fastener;

FIG. 6 is a view similar to FIG. 3 of the modified fastener.

It is observed that fasteners of this kind are normally made of theorder of 5 or 10 mm diameter overall, and say 7 mm-15 mm in length,which small size aggravates the problems of providing accurate shapesand contours of different parts in mass production. It is also observedthat the drawings are many times full size.

Referring to the drawings, the fastener comprises a body with a largestdiameter generally cylindrical portion 10, a slightly smaller diametergenerally cylindrical portion 12, a third and again smaller diametercyllindrical portion 14 and a pilot portion, also generally cylindricalindicated by the reference numeral 16 which is slightly smaller indiameter than the portion 14. The pilot portion is bevelled at theleading end at 18.

The successive parts 10, 12, 14, 16 are separated by relatively narrowflat bottom grooves 20 all of which may be of the same diameter.

The portions 10, 12 and 14 are provided with generally helicallyextending ribs shown in cross-section in FIG. 4 and, as previouslyexplained, these may not be symmetrical. As here illustrated the upperflank 22 most closely adjacent the end 10 is steep and lies at only aslight angle to that of a plane normal to the axis of the completefastener whereas the opposing flank 24 is relatively gently inclined,all for the purpose of improving the insertion and the pull-out loadapplied for example in the direction of the arrow A when the fastener isinstalled with the end 10 flush with the surface of the article.

The helix angle B is preferably less than 45° to a plane normal to theaxis for the purpose of increasing the anti-rotational hold. The helixangle of the teeth on the portions10, 12 and 14 may be equal, but ofcourse different since the portions are of different hands.

As best seen in FIGS. 1 and 3 a pair of diametrically related flats 30is provided. The diameter D (FIG. 1) between the flats may be the same(within overlapping manufacturing tolerances) as the cylindricaldiameter of the portions 20, in which case it will be appreciated thatthere are separate flats provided on each of the portions 12 and 14 butnot on the portions 20.

However, if the portions 20 are of different diameters along the lengthof the fastener, as may be the case, there may be flats on the portions20. A typical case is shown in the drawings.

As previously explained, this fastener is to be manufactured bydie-casting by injecting molten material, most usually metal, preferablyas a pressure die-casting rather than a gravity die-casting, into anappropriate die cavity which may be formed between a pair of die partsmeeting at a plane indicated by the chain dot line P FIG. 1 and 3. Theplane bi-sects the flats.

This means that in removal of material from a block to form a die cavitycorresponding to one half of the fastener, the grooves which are to formthe helical ribs run out short of the face of that block which is toform the mating face with another similar block forming the other halfthe die cavity, and in production, the other half of the fastener. Thisgreatly simplifies die production and in particular it means that theroot or crest 32 (FIG. 3) of one rib on one side of the flat needs onlyto be generally and not precisely aligned with the like root or crest 34on the opposite side of the same flat. In one modification, not shown,end portion 10 has an added hexagonal head of larger diameter across theflats than the body across its flats, or of the same across-flatsdimension. In another modification not shown, the hexagon head is usedinstead of portion 10 and the groove 20 between the head and portion 12is omitted: that is to say there are only two ribbed or toothedportions.

The drawings do not show the screwthread portion which the fastener isto be provided with, either as a nut or stud as mentioned. However, thefastener made by the die-casting method as shown in the drawings is tobe gripped by the flats and/or by the hexagon head (if provided) to beoperated on by a tapping or threading machine. The die-casting willprovide a hole to be screw-tapped, or a stud to be screw-threaded.

In another modification, not shown, the head 10 is omitted. In anothermodification, not shown, portions 12, 14 are of equal diameter. In athird modification, not shown, the fastener is double-ended, that is tosay it has pilot portions 16 at each end and no head and both ribbedportions of the same diameter.

Knurling, particularly to provide generally frusto-pyramidal teeth maybe employed instead of ribs on some or all of the portions. Asmentioned, the rib angle (where ribs are used) or the knurl angle isvariable between 0% and 90% to the fastener axis.

I claim:
 1. A diecast fastener suitable for being installed in aninstallation material and having a longitudinal axis comprising:(a) abody portion having first and second sections, the first section beingsubstantially diametrically opposite to the second section on thefastener, the first section having helically-oriented ribs orientedagainst one direction of rotation of the fastener and the second sectionhaving helically-oriented ribs oriented against the opposite directionof rotation of the fastener, the body portion further having first andsecond flats defining first and second planes, the first and secondsections being separated by the first and second flats on the fastener,the ribs not extending from the fastener beyond the first and secondplanes; and (b) a pilot portion of lesser diameter in cross-section thanthe body portion, the pilot portion being located at one end of thefastener for guiding the fastener into the installation material.
 2. Thediecast fastener or claim 1 further comprising a bottom groove of lesserdiameter in cross-section than at least a portion of the pilot portion,the bottom groove being disposed between the pilot portion and the bodyportion so that the pilot portion tends to prevent the fastener frombeing pulled out of the installation material in a direction parallel tothe longitudinal axis of the fastener.
 3. The diecast fastener or claim1 comprising a plurality of body portions.
 4. The diecast fastener ofclaim 1 comprising a plurality of body portions, two of the bodyportions having different diameters in cross-section.
 5. The diecastfastener of claim 1 wherein the ribs have resisting plane surfacesinclined toward an end of the fastener opposite the pilot portion, theresisting plane surfaces being substantially perpendicular to thelongitudinal axis of the fastener so as to tend to prevent the fastenerfrom being pulled out of the installation material.
 6. The diecastfastener of claim 1 wherein the ribs have facilitating plane surfacesinclined toward an end of the fastener having the pilot portion, thefacilitating plane surfaces being at a relatively small angle to thelongitudinal axis of the fastener so that the installation of thefastener is facilitated.
 7. The diecast fastener of claim 1 furtherincluding a screw-threaded portion for attaching objects to the fastenerwhen the fastener is installed.
 8. The diecast fastener of claim 7wherein the screw-threaded portion is inside the fastener.
 9. Thediecast fastener of claim 7 wherein the screw-threaded portion extendsfrom and is outside the fastener.
 10. The diecast fastener of claim 1wherein helical orientation of the ribs is at a 45 degree angle to aplane normal to the longitudinal axis of the fastener.
 11. The diecastfastener of claim 1 wherein the ribs are knurled.
 12. The diecastfastener of claim 1 wherein the ribs of the first section and the ribsof the second section are oriented against both directions of rotation.13. The diecast fastener of claim 12 wherein the ribs of the first andsecond sections are cross-knurled.
 14. The diecast fastener of claim 1wherein the fastener is from 5 to 10 millimeters in diameter and from 7to 10 millimeters in length.
 15. The diecast fastener of claim 1 whereinthe body portion has cross-sections substantially consisting of two arcsof the same radius joined by substantially parallel secants on a singlecenter of curvature.
 16. The diecast fastener of claim 3 furthercomprising a plurality of bottom grooves, of lesser diameter incross-section than the body portions, disposed between the bodyportions.
 17. A diecast fastener suitable for being installed in aninstallation material and having a longitudinal axis comprising:(a) afirst body portion having first and second sections, the first sectionbeing substantially diameterically opposite to the second section on thefastener, the first and second sections having helically-oriented ribsoriented against a first direction of rotaton of the fastener, the firstbody portion further having first and second flats defining first andsecond planes, the first and second sections being separated by thefirst and second flats on the fastener, the ribs of the first and secondsections not extending from the fastener beyond the first and secondplanes; (b) a second body portion having third and fourth sections, thethird section being substantially opposite to the fourth section on thefastener, the third and fourth sections having helically-oriented ribsoriented against a second direction of rotation opposite to the firstdirection of rotation, the second body portion further having third andfourth flats defining third and fourth planes, the third and fourthsections being separated by the third and fourth flats on the fastener,the ribs of the third and fourth sections not extending from thefastener beyond the third and fourth planes; and (c) a pilot portion oflesser diameter in cross-section than the body portions, the pilotportion being located at one end of the fastener for guiding thefastener into the installation material.
 18. The diecast fastener ofclaim 15 further comprising a bottom groove of lesser diameter incross-section than the pilot portion, the bottom groove being disposedbetween the pilot portion and the body portions so that the pilotportion tends to prevent the fastener from being pulled out of theinstallation material in a direction parallel to the longitudinal axisof the fastener.
 19. The diecast fastener of claim 15 further includingat least one additional body portion.